Liquid water is created inside a fuel cell for at least two fundamental reasons: (1) the creation of water during the electrochemical reaction, and (2) the condensation of incoming water vapor entering with humidified reaction gases. The amount of water created during the electrochemical reaction depends directly on the current density. The amount of incoming water vapor that condenses inside the gas flow channels of the collector plates depends on the operating conditions such as stoichiometry and the relative humidity of the incoming gas streams. Excess liquid water in the cell can partially block the gas flow fields creating what is known as “flooding.”
Referring now to FIG. 1, many prior art fuel cells have been constructed using a solid polyelectrolyte membrane 12 having a cathode face 14 and an opposite anode face 16. A cathode electrode 18 including a catalyst supported on carbon particles, and an ionomer is formed on the cathode face 14 of the membrane 12. Similarly, an anode electrode 20 including a catalyst supported on carbon particles, and an ionomer is formed on the anode face 16 of the membrane 12. A microporous layer 22 may be provided over the cathode electrode 18. A gas diffusion media 24 may be provided over the microporous layer 22. A collector plate 26 is provided over the gas diffusion media 24, and wherein the collector plate 26 includes a plurality of lands 28 and channels 30 defining a reactant gas flow field. In this case, a reactant gas such as oxygen or air is provided through the channels 30 and diffuses through the gas diffusion media 24 and microporous layer 22 so that the cathode electrode 18 catalyzes the reaction of oxygen molecules with hydrogen protons to produce water. Such prior art fuel cell products are typically constructed to allow for the reaction produced water to diffuse through the microporous layer 22 and gas diffusion media 24. However, the water can begin to accumulate underneath the lands 28 of the bipolar plate 26 and result in a liquid layer 34 forming in the channel 30, which is known as “flooding.” The flooding prevents the reactant gases from flowing towards the membrane 12 and thus adversely impacts fuel cell performance.